1. Field of the Invention
The present invention relates generally to a molten magnesium supply system as well as to a molten magnesium supply method, and in particular, to a molten magnesium supply system that is constituted with a molten magnesium supplying apparatus for a die casting machine of a cold chamber type for casting molten magnesium (with molten magnesium alloy inclusive), or includes a melting and holding furnace for melting a magnesium ingot and holding molten magnesium to be supplied to an injection sleeve of a die casting machine, or an ingot charging apparatus for charging a preheated magnesium ingot into a melting and holding furnace, as well as to a molten magnesium supply method that includes charging a preheated magnesium ingot into a melting and holding furnace, melting the ingot in the furnace, holding molten magnesium in the furnace, and supplying molten magnesium to an injection sleeve of a die casting machine.
2. Description of the Related Art
Cold-chamber die casting needs fresh and homogeneous molten metal to be continuously and instantaneously injected under high pressure into recesses of a cavity in a mold. For such injection, the die casting machine has an injection sleeve, and is provided with a supply system for supplying molten metal to the injection sleeve. The supply system is adapted for a conforming supply of molten metal meeting various requirements, such as for molten metal amount or quantity to be accurate and nature or quality to be controlled and stable in consideration of molding conditions.
In the case of magnesium, the molten metal has a significant tendency to be oxidized, and needs an air-free supply to the injection sleeve via pipe, duct, etc. For such supply, one may employ a molten metal transfer mechanism or molten metal transferring means for forcing molten metal to advance in a molten metal transfer pipe. The molten metal transfer mechanism or molten metal transferring means may be of a volume displacement type such as by use of a screw pump, or of a fluid streaming type such as by use of an electromagnetic pump in which a fluid flow rate is controlled with an electric current in an exciting coil around a fluid circuit.
A typical molten magnesium supply system is constituted with a molten magnesium supplying apparatus including a melting and holding furnace and sometimes provided with a preheater for preheating a magnesium ingot.
FIG. 1 illustrates a conventional molten metal supply system. The system comprises a furnace body Fb of a xe2x80x9cmagnesium melting and/or molten magnesium holding furnace (hereinafter sometimes called xe2x80x9cmolten metal furnacexe2x80x9d) 55 and a molten metal transfer pipe 52 extending therefrom. The transfer pipe 52 is constituted at a suction inlet end thereof with an outlet port Fp of the furnace 55 communicating with an inside of the furnace body Fb, and along the remaining length thereof with a heated transfer tube Tb flange-joined to the port Fp. An electromagnetic pump 50 is installed on the inlet end of the pipe 52. The transfer pipe 52 is formed at a delivery end thereof with a downwardly bent portion 52a, which has a downward opening 52b as a supply outlet matching in position with an upward reception opening 51a of an injection sleeve 51.
Molten magnesium M in the molten metal furnace 55 receives a constant leveling, whereby a xe2x80x9csurface level of molten magnesiumxe2x80x9d (hereinafter called xe2x80x9cmelt levelxe2x80x9d or simply xe2x80x9clevelxe2x80x9d) B in the furnace 55 is controlled so that a melt level A in the transfer pipe 52, which is equivalent to the level B, is maintained near xe2x80x9ca height of a bottom point of an inner circumference at a top of tube wallxe2x80x9d (hereinafter sometimes called xe2x80x9cdelivery heightxe2x80x9d or simply xe2x80x9cheightxe2x80x9d) of the delivery end portion 52a. 
In the above-noted system, molten magnesium M flowing in the pipe 52 is subjected to a flow resistance at both suction and delivery sides of the electromagnetic pump 50. The flow resistance of pipe 52 is small, but increases with foreign materials sticking on the wall or mixed in metal. In this case, if the coil current of the pump 50 is constant, the pump 50 delivers a reduced amount of molten metal.
To keep the delivery rate free from unfavorable influences of conditions in the transfer pipe 52, a throttle 53 is installed at a flange joint portion 52d of the pipe 52, and fixed thereto. The throttle 53 provides a sufficient flow resistance for the pump 50 to deliver a corresponding flow rate of molten metal, allowing for the transfer pipe 52 to supply the flow rate of molten metal.
Accordingly, in this molten metal supply system empolying an electromagnetic pump, a metering accuracy of molten metal can be maintained high by exchanging the fixed throttle 53 to another one or cleaning the same.
In order to prevent molten magnesium M from being oxidized, an injection opening 52c for injecting anti-oxidization gas G for the molten magnesium M is provided at a top portion of the delivery end portion 52a. Anti-oxidization gas G injected from the injection opening 52c is filled in a space defined by molten metal of the melt level A and the wall of to the delivery end portion 52a of the transfer pipe 52, so that molten metal M to be supplied to the injection sleeve 51 is prevented from oxidization. The anti-oxidization gas G is also injected in the molten metal furnace 55, and a space above the melt level B in the furnace 55 is filled with the gas G.
As the anti-oxidization gas G, there is used a diluted antideflagrant gas in which sulfur hexafluoride (hereinafter referred to as xe2x80x9cSF6xe2x80x9d) is diluted with dried air, or an inert gas such as argon.
In FIG. 1, reference numeral 54 denotes a heater, reference numeral 57 denotes an injection plunger driven in a reciprocating manner within the injection sleeve 51 by a hydraulic operation mechanism 58, and reference numeral 59 denotes a metal mold cavity communicating with the injection sleeve 51.
In the conventional molten metal supply system empolying an electromagnetic pump, however, as the throttle 53 is fixed to the flange joint portion 52d of the transfer pipe 52, there occur needs of pipe disconnection for maintenance services, such as for cleaning to the throttle 53 or pipe wall therearound or for replacement of the throttle 53. In particular, in the case of molten magnesium (including molten magnesium alloy), the molten metal tends to be oxidized or combusted during such a service.
Though one of SF6 dilute antideflagrant gas and an inert gas such as argon is generally used as anti-oxidization gas G, such a use of single gas has a potential possibility of causing molten metal oxidization or loose ending or cut of molten metal supply. There is a problem of increased oxidization, followed by difficulty in maintenance work, and a supply amount of molten metal becomes unstable, so that a stable die casting work can not be performed.
That is, SF6 dilute antideflagrant gas is relatively inexpensive and has a high antideflagrant effect owing to a high dilution rate thereof. However, when molten magnesium M is transferred to the injection sleeve 51 by the electromagnetic pump 50, oxidization of the molten magnesium M and/or reaction product is easy to occur and the ending of molten magnesium supply at the opening 52b of the delivery end portion 52a becomes sharp.
An inert gas such as argon is used alone, which becomes relatively expensive, however, oxidization of the molten magnesium M is reduced and the ending of molten magnesium supply is improved. In an ordinary use, however, the antideflagrant nature is relatively inferior, and there is a problem that, when the melt level M in the molten metal furnace 55 varies at an ON/OFF time of the constant melt level control and external air enters in/leaves from the molten metal furnace 55, the molten magnesium M sticking on an inner surface of the delivery end portion 52a is oxidized.
Furthermore, in the conventional molten metal supply system empolying an electromagnetic pump, as the delivery end portion 52a of the transfer pipe 52 is bent downwards, delivered molten magnesium M falls into the injection sleeve 51, where it has turbulent streams. Turbulent streams accompany air inclusion into molten metal M, causing oxidization and combustion of molten magnesium M, with an increased quantity of reaction products such as oxides, constituting a difficulty of maintenance, rendering supply molten metal amount unstable. As a result, a stable die casting work can not be obtained.
Also, in a conventional melting and holding furnace, a crucible having a bath tab shape is partitioned into a melting chamber and a holding chamber by a partition plate. In this case, the melting chamber is cold-charged (ingot is thrown and melted in the melting chamber) and molten magnesium is transferred to the holding chamber via the partition plate. A transfer pipe is provided downward of the holding chamber, and molten magnesium is filled in the transfer pipe.
In Japanese Patent Publication No. 3-37462, there has been disclosed a temperature holding furnace provide with a transfer pipe for supplying molten metal to an injection sleeve in a die casting machine. The temperature holding furnace has a structure in which molten metal is hot-charged from another melting furnace, and the furnace itself is maintained horizontally during die casting work and it is maintained together with the transfer pipe in its tilted position during stopping of die casting work.
In these cases, when the molten metal to be applied is magnesium alloy, as it has a tendency to rapidly produce oxide with air in contact, oxidization of the metal can be suppressed in a state in which a space in the transfer pipe is filled with antideflagrant gas, which results in improvement in quality of die cast product.
In the latter temperature holding furnace, molten metal in the transfer pipe can be transferred by holding the temperature holding furnace as well as the transfer pipe in the tilted position so that easiness in such a work as maintenance can be achieved. In the conventional melting and holding furnace or temperature holding furnace, however, when a cold charge or a hot charge is conducted, disturbance occurs in molten magnesium portion around charged portion, air is involved in molten magnesium due to this disturbance, and the molten magnesium is oxidized, so that much dross/sludge occurs due to this oxidization. There is a drawback that, since molten magnesium including this dross/sludge is transferred to the transfer pipe portion via the holding chamber, which results in troubles inside the transfer pipe and/or bad quality products.
Also, in the conventional melting and holding furnace, as the transfer pipe is fixed in a horizontal position, when it is required to discharge molten magnesium contained in the transfer pipe at a time of maintenance or the like, it is not only made impossible to discharge molten magnesium remaining in the transfer pipe completely but also it is required to handle some molten magnesium sufficiently carefully, which results in difficulty in maintenance work.
Furthermore, in the melting and holding furnace, as one crucible serves as the melting chamber and the holding chamber, there are two cases, namely cold charge is being effected in the melting chamber side and it is not being effected. Due to these two cases, there occurs a drawback that, when the temperature of the molten magnesium in the holding chamber is controlled, it becomes difficult to maintain molten magnesium in the holding chamber in a constant temperature without temperature variation, and fluidic characteristic of molten magnesium varies due to temperature variation so that supply amount of molten magnesium is made unstable and, therefore, die cast products of a good quality can not be secured in a stable manner.
A first conventional method or a second conventional method is employed for charging a magnesium ingot to a melting and holding furnace. In the first conventional method, a rack for preheating is placed on a melting and holding furnace and a magnesium ingot is manually thrown into molten magnesium. In the second conventional method, when a preheated magnesium ingot placed with a lying position in which its longitudinal axis is horizontal is automatically charged from a preheating apparatus to a melting and holding furnace, it is pushed on such guide means as a rolling type conveyor and thrown by a cylinder so as to fall in the melting and holding furnace.
In the first conventional method, a degree of freedom for throwing is high to some extent, but first a worker is always required therefor and secondly a furnace lid can not be put in an opened state for a long time in view of radiation heat from the melting and holding furnace and/or oxidization of molten magnesium.
In the second conventional method, as an ingot falls in molten magnesium with nonstop, a molten magnesium melt level and antideflagrant gas atmosphere are disturbed.
In the first and second conventional methods, thus, generation of dross/sludge is increased due to the disturbances of the molten magnesium melt level and the antideflagrant gas atmosphere, so that a problem or defect occurs in the quality of die cast products obtained.
When the furnace lid is opened for a long time, the temperature of molten magnesium is lowered and, when die casting is performed in a die casting machine, fluidity of molten magnesium deteriorates and varies due to the temperature lowering. As a result, a problem or defect occurs in the quality of die cast products.
Furthermore, a variation of melt level corresponding to one magnesium ingot and acceleration of vertical movement of melt surface due to falling of a magnesium ingot with nonstop acts as dynamic pressure variation in a molten metal transfer pipe, for example, in a molten magnesium supply system employing an electromagnetic pump. There are also a drawback in which the dynamic pressure in the transfer pipe adversely affects metering accuracy for the delivery amount of molten magnesium.
A first object of the present invention is to provide a molten magnesium supply system including a molten magnesium supplying apparatus which has an excellent easiness in maintenance work or in which the supply amount of molten magnesium is made stable so that a stable die casting work can be obtained.
A second object of the invention is to provide a molten magnesium supply system including a melting and holding furnace with a tilting mechanism in which maintenance work can be made easy and dross/sludge occurring in a melting chamber can be effectively prevented from moving to a holding chamber, and temperature of molten magnesium in the holding chamber can be controlled with a high accuracy, so that die cast products of a good quality can be obtained in a stable manner.
A third object of the invention is to provide a molten magnesium supply system including an ingot charging apparatus, and a molten magnesium supply method in which automatic charge of a magnesium ingot is allowed in a state in which oxidization of molten magnesium, temperature lowering of the molten magnesium and melt level variation are suppressed to the utmost, thereby improving and stabilizing the quality of die cast product.
The present invention has been made with such points in view.
To achieve objects, an aspect of the present invention provides a molten magnesium supply system including a molten metal furnace put under a melt level control, a molten magnesium supplying apparatus comprising a molten metal transfer pipe communicating at one end thereof with the molten metal furnace, the molten metal transfer pipe having at another end thereof an ascending bent pipe portion as a deliver) portion for delivery of molten magnesium to be supplied to an injection sleeve, and molten metal transferring means for forcing molten magnesium from the molten metal furnace to be transferred in the molten metal transfer pipe and delivered through the delivery portion, and gas supplying means for supplying an anti-oxidization gas to vacant spaces in the molten metal furnace and the molten metal transfer pipe, wherein the molten metal transfer pipe is provided with a funnel portion communicating with the delivery portion, for receiving delivered molten magnesium from the delivery portion and supplying received molten magnesium to the injection sleeve.
According to this aspect, a melt level of molten magnesium in a molten metal transfer pipe is maintained at a delivery height of a bent pipe portion close to a funnel portion according to a melt level control in a molten metal furnace. Molten magnesium is delivered from a delivery portion of the molten metal transfer pipe to the funnel portion, as it is forced to be transferred by molten metal transferring means, and delivered molten magnesium is wholly supplied to an injection sleeve.
In a molten magnesium supply system according to any applicable aspect herein, the bent pipe portion may preferably be reduced to have a throttle part.
In a molten magnesium supply system according to any applicable aspect herein, the funnel portion may preferably comprise a communication part for communication with the bent pipe portion, a supply hole for supplying received molten magnesium to the injection sleeve, and a lower part extending between the communication part and the supply hole, the lower part having an inside surface gradually reduced in diameter and smoothly bent between the communication part and the supply hole.
In this case, a melt level of molten magnesium in a molten metal transfer pipe is maintained at a delivery height of a bent pipe portion according to constant melt level control in a molten metal furnace, close to a funnel portion. Molten magnesium is delivered from a delivery end of the molten metal transfer pipe to the funnel portion by molten metal transferring means and the whole delivered amount of molten magnesium is supplied to an injection sleeve.
Since supplying molten magnesium to the injection sleeve is performed from the melt level of molten magnesium close to a supply hole of the funnel portion, a flowing-out head of the molten magnesium can be made small. Since the inside surface of a lower part of the funnel portion is gradually reduced in inside diameter and bent smoothly, it is formed in a smooth flowing-out sloped surface and molten magnesium is supplied to the injection sleeve in a turbulence-reduced state. Accordingly, oxidization of the molten magnesium and reaction product therewith are prevented from occurring at the supply end and troubles such as combustion, blocking, staying, and the like due to such an occurrence are also prevented, so that molten metal supply to the injection sleeve can be sharply ended. Thus, the molten magnesium supplying apparatus has an excellent easiness in maintenance work, and a supply amount of molten magnesium is made stable so that a stable die casting work can be performed.
In a molten magnesium supply system according to any applicable aspect herein, the supply hole of the funnel portion may preferably be provided with a shutter for closing the supply hole.
In this case, the shutter can block a residue drip from the supply hole.
In a molten magnesium supply system according to any applicable aspect herein, the funnel portion may preferably be formed with an upper opening and provided with a lid for closing the upper opening.
In this case, the lid can be attached to or detached from an upper opening of the funnel portion, permitting a facilitated maintenance and cleaning to the funnel portion, allowing an improved maintenance service and a stable supply of molten magnesium.
In a molten magnesium supply system according to any applicable aspect herein, the gas supply means may preferably comprise a first gas supply line for supplying an inert gas as the anti-oxidization gas, a second gas supply line for supplying a sulfur hexafluoride dilute antideflagrant gas as the anti-oxidization gas, and control means for supplying a vacant space of the funnel portion with the inert gas when the melt level control to the molten metal furnace is on, and with the sulfur hexafluoride dilute antideflagrant gas when the melt level control is off.
In this case, a melt level of molten magnesium within a molten metal transfer pipe is maintained at a delivery height of a bent pipe portion and close to a funnel portion. An amount of molten magnesium is transferred by the molten metal transferring means, and is delivered from the delivery portion of the molten metal transfer pipe to the funnel portion so that delivered molten magnesium is wholly supplied to an injection sleeve.
When the melt level control to the molten metal furnace is turned on, an inert gas is filled in a vacant space of the funnel portion, whereby the delivered molten magnesium is kept from oxidization and in free of reaction products due to such oxidization, thus allowing the ending of molten magnesium supply to be quick and sharp, so that supply of molten magnesium to the injection sleeve is rendered stable.
When the melt level control is turned off at the molten metal furnace, a sulfur hexafluoride dilute antideflagrant gas is filled in a vacant space that the funnel portion then has, so that oxidization and combustion of molten magnesium is prevented over an off-duty period of molten magnesium supply, and molten magnesium left in the transfer pipe is kept free from magnesium oxides that otherwise might have been produced by such oxidization or combustion. Such oxides would have adhered to or deposited on the wall of the transfer pipe. As a result, molten magnesium supply is allowed to be ended sharp. Maintenance to the system is facilitated. A necessary supply amount of molten magnesium is secured, ensuring a conforming die casting.
In a molten magnesium supply system according to any applicable aspect herein, the control means may preferably comprise a control valve operative with a control command for the melt level control.
In this case, switching-over of gases to be supplied can be automatically controlled with a control command for melt level control, allowing a more excellent easiness in maintenance work and a more stable supply of molten magnesium.
In a molten magnesium supply system according to any applicable aspect herein, the molten metal transferring means may preferably comprise a volume replacement transfer mechanism.
In this case, a desirable amount of molten magnesium can be secured in transfer.
In a molten magnesium supply system according to any applicable aspect herein, the molten metal transferring means may preferably comprise a fluid streaming transfer mechanism.
In this case, a controlled amount of molten magnesium can be transferred in a flexible manner.
In a molten magnesium supply system according to any applicable aspect herein, the fluid streaming transfer mechanism may preferably comprise an electromagnetic pump.
In this case, molten magnesium is transferred along the transfer pipe by the electromagnetic pump, which may be automatically controlled in synchronism with the melt level control of the molten metal furnace.
In a molten magnesium supply system according to any applicable aspect herein, the molten metal furnace may preferably comprise a melting and holding furnace including a crucible member provided with a melting chamber heated for melting magnesium and a holding chamber heated for holding molten magnesium, the melting chamber communicating with the holding chamber at a bottom region of the crucible member deeper in the melting chamber than in the holding chamber, the holding chamber communicating with the one end of the molten metal transfer pipe.
In this case, a cold-charged magnesium block may be melted in a melting chamber. Streams of heavier molten magnesium tend to be stagnant at a bottom of the melting chamber, where they are advantageously kept from flowing through a holding chamber into the molten metal transfer pipe.
In a molten magnesium supply system according to any applicable aspect herein, the melting and holding furnace may preferably include a tilting mechanism for tilting the crucible member together with the molten metal transfer pipe.
In this case, the transfer pipe can be tilted relative to a melt level to expel molten magnesium, as necessary for maintenance service.
In a molten magnesium supply system according to any applicable aspect herein, the melting chamber may preferably have a round bottom, and the holding chamber may preferably have a flat bottom.
In this case, insufficiently heated molten magnesium has an increased stagnant tendency in a round bottom, and sufficiently heated molten magnesium has an increased flowing tendency on a flat bottom.
In a molten magnesium supply system according to any applicable aspect herein, the melting and holding furnace may preferably include a gas burner for heating the melting chamber and an electric heater for heating the holding chamber.
In a molten magnesium supply system according to any applicable aspect herein, the molten metal furnace may preferably comprise a melting and holding furnace for melting a preheated magnesium ingot and holding molten magnesium, and the molten magnesium supply system may preferably comprise ingot charging means for charging the preheated magnesium ingot into the melting and holding furnace, keeping the preheated magnesium ingot substantially free from contact with air.
In this case, a preheated magnesium ingot can be charged into a melting and holding furnace, without unfavorable contact with air, allowing for molten magnesium of a secured quality to be supplied.
In a molten magnesium supply system according to any applicable aspect herein, the molten magnesium supply system may preferably comprise a preheater for preheating a magnesium ingot to provide the preheated magnesium ingot in an oxidant-free atmosphere, and the ingot charging means may preferably be adapted for discharging the preheated magnesium ingot from the prehater, keeping the preheated magnesium ingot substantially free from contact with air.
In this case, a preheated magnesium ingot can be discharged from a preheater, without unfavorable contact with air, allowing for the ingot to be handled in a fresh state.
In a molten magnesium supply system according to any applicable aspect herein, the ingot charging means may preferably be adapted for carrying the preheated magnesium ingot between the preheater and the melting and holding furnace, keeping the preheated magnesium ingot substantially free from contact with air.
In this case, a preheated magnesium ingot can be carried between the preheater and the melting and holding furnace, without unfavorable contact with air, allowing for the ingot to be charged in a fresh state.
In a molten magnesium supply system according to any applicable aspect herein, the ingot charging means may preferably comprise a chuck for chucking the preheated magnesium ingot, a carrier for carrying the chuck, a hood for covering the chuck and the preheated magnesium ingot, and gas supply means for supplying an anti-oxidization gas inside the hood.
In this case, supplied anti-oxidization gas protects a preheated magnesium ingot from unfavorable contact with ambient air about a hood.
Further, to achieve the first aspect, another aspect of the invention provides a molten magnesium supply system including a molten metal furnace put under a melt level control, a molten magnesium supplying apparatus comprising a molten metal transfer pipe communicating at one end thereof with the molten metal furnace, the molten metal transfer pipe having at another end thereof an ascending bent pipe portion as a delivery portion for delivery of molten magnesium to be supplied to an injection sleeve, and molten metal transferring means for forcing molten magnesium from the molten metal furnace to be transferred in the molten metal transfer pipe and delivered through the delivery portion, and gas supplying means for supplying an anti-oxidization gas to vacant spaces in the molten metal furnace and the molten metal transfer pipe, wherein the bent pipe portion is reduced to have a throttle part.
According to this aspect, upon delivery of molten magnesium from a delivery portion that is an ascending bent pipe portion of a molten metal transfer pipe, molten magnesium flowing in bent pipe portion is subjected to a flow resistance of a throttle part, having a head loss developed thereacross. As the flow resistance can be set in a voluntary manner, the head loss can be large enough to substantially control delivery rate of molten magnesium without employing a conventional throttle fixed to a flange joint portion at a suction end.
To achieve the second object, another aspect of the invention provides a molten magnesium supply system including a melting and holding furnace with a tilting mechanism comprising a melting and holding furnace section constituted with a crucible whose interior is partitioned to a holding chamber and a melting chamber by a partition portion such that molten magnesium is mutually movable between the holding chamber and the melting chamber, the bottom portion of the melting chamber being lower than the bottom portion of the holding chamber, and heating means being respectively provided for heating the holding chamber and the melting chamber exclusively, a molten metal supplying apparatus provided so as to communicate with the holding chamber, for supplying molten magnesium into an injection sleeve of a die casting machine, and a tilting mechanism for holding the melting and holding furnace section horizontally and for, as occasion demands, tilting the melting and holding furnace section together with the molten metal supplying apparatus upwardly about the melting chamber serving as a tilting fulcrum to hold the same in the tilted position.
According to this aspect, dross/sludge generated in a melting furnace and/or molten magnesium with a relatively high specific gravity which has just been cold-charged to melt down are deposited or stayed on a bottom of the melting chamber due to a difference in height between a bottom portion of a holding chamber and the bottom portion of the melting chamber and they can be prevented from moving the holding chamber.
Also, respective temperature controls of molten magnesium respectively contained in the holding chamber and the melting chamber can be performed by respective exclusive heating means regardless of temperatures of the molten magnesium in the respective adjacent chambers. Accordingly, the temperature control of molten magnesium in the holding chamber can be performed with a high accuracy by the exclusive heating means regardless of absence/existence of cold-charge, and die cast products a good quality of can be obtained in a stable manner.
When the melting and holding furnace section is tilted together with a molten metal supplying apparatus to be held in the tilted position, molten magnesium in the molten metal supplying apparatus can be delivered to a crucible without staying. Accordingly, easiness in maintenance work can be obtained.
In a molten magnesium supply system according to the above aspect, the holding chamber may preferably be formed at the bottom portion thereof in an approximate flat bottom, the melting chamber may preferably be extended from the approximate flat bottom and formed in a downwardly concave round bottom, and the heating means may preferably be constituted with an electric heater for the holding chamber and a gas burner for the melting chamber.
In this case, dross/sludge generated in a melting chamber and/or molten magnesium with a relatively high specific gravity, as it has just been molten from a cold-charged block, are stayed or deposited in a round bottom of a melting chamber owing to a difference in shape between a bottom of a holding chamber and the melting chamber, so that they are kept from being carried into the holding chamber.
Temperature of molten magnesium in the holding chamber can be controlled with a high accuracy by a readily controllable electric heater, and magnesium ingot charged to the melting chamber can melt in a short while with an efficient hot heating of the round bottom by a gas burner. Accordingly, die cast products can be obtained with a secured quality.
As the bottom of the melting chamber is shaped in a round form, melting work in which supply of molten magnesium is not performed can be effected with a position of the melting and holding furnace held in an inclination state, so that dross/sludge generated during melting work and molten magnesium having a relatively high specific gravity which has just been melted down can almost completely be prevented from being transferring to the holding chamber. Accordingly, troubles which may occur in an interior of a molten metal supplying apparatus are suppressed so that maintenance work can be facilitated and die cast products of a good quality can be obtained in a more stable manner.
To achieve the third object, another aspect of the invention provides a molten magnesium supply system including an ingot charging apparatus for charging a preheated ingot from a preheating apparatus to a melting and holding furnace, the system comprising conveying means for holding the preheated magnesium ingot by an ingot chuck to discharge the same from the preheating apparatus and for conveying the discharged magnesium ingot to charge the same into the melting and holding furnace, and a hood mounted to the conveying means, which communicates with an ingot discharge port of the preheating apparatus and an ingot charge port of the melting and holding furnace respectively at an ingot discharge time and at an ingot charge time of the preheated magnesium ingot to form closed spaces for allowing ingot discharge operation of the ingot chuck and allowing charge operation thereof, and which covers the preheated magnesium ingot held by the ingot chuck during conveyance.
According to this aspect, a preheated ingot can be charged from a preheating apparatus to a melting and holding furnace by conveying means without manual operation.
As discharge of the preheated ingot from the preheating apparatus and charge thereof to the melting and holding furnace are performed by an ingot chuck operated within closed spaces defined by a hood, immersion of air, disturbance or flowing-out of antideflagrant gas in the melting and holding furnace and heat dissipation form the melting and holding furnace can be suppressed.
As the preheated magnesium ingot is covered with the hood during conveyance from the preheating apparatus to the melting and holding furnace, heat dissipation from the magnesium ingot is suppressed and temperature lowering of the ingot itself can be suppressed to the utmost. By the provision of an ingot charging apparatus, a preheated magnesium ingot can automatically be charged to the melting and holding furnace, so that oxidization of molten magnesium, temperature lowering of the molten magnesium, and variation in molten surface are suppressed to the utmost. As a result, the ingot charging apparatus contributes to an improvement in quality of die cast products, allowing for a secured quality.
In a molten magnesium supply system according to the above aspect, the hood may preferably have a gas injection port for antideflagrant gas.
In this case, charge of a preheated magnesium ingot to a melting and holding furnace can be carried out while antideflagrant gas is injected into a closed space defined by a hood. Oxidization of molten magnesium is suppressed by injection of the antideflagrant gas, allowing a decrease in charge speed of the ingot. Corresponding to the decrease, variations in molten magnesium temperature and/or disturbances of molten magnesium melt level and of antideflagrant gas atmosphere can be suppressed. Accordingly, die cast products can be improved with a secured quality.
To achieve the third object, another aspect of the invention provides a molten magnesium supply method including charging a preheated magnesium ingot by using an ingot charging apparatus according to the above aspect, wherein the preheated magnesium ingot is held by the ingot chuck in a longitudinal position where its longitudinal axis is vertical to be discharged from the preheating apparatus by the conveying means and to be conveyed to the melting and holding furnace, and, after most portion of the magnesium ingot is immersed in molten magnesium in the melting and holding furnace by a vertical downward operation of the ingot chuck at a low speed in a state in which the closed space defined by the hood communicating with the ingot charge port of the melting and holding furnace is filled with the antideflagrant gas injected from the gas injection port, the magnesium ingot is released into the melting and holding furnace.
According to this aspect, as a preheated magnesium ingot can enter in a melting and holding furnace from an ingot charge port in a longitudinal position where its longitudinal axis is vertical, the ingot charge port can be set such that its opening area is small, and correspondingly heat dissipation from the melting and holding furnace can be suppressed.
Immersion of the preheated magnesium ingot to molten magnesium is carried out by vertical downward operation of an ingot chuck at a low speed in a state in which a closed space is filled with antideflagrant gas, namely the immersion can be performed in a state in which oxidization of molten magnesium, variation in molten magnesium temperature, and disturbances of a molten magnesium melt level and a antideflagrant gas atmosphere are suppressed. Accordingly, an ingot charging method can be provided to improve and stabilize quality of die cast products.
Another aspect of the invention provides a molten magnesium supply method comprising the steps of chucking a preheated magnesium ingot in a suspended position, keeping the chucked magnesium ingot free from contact with air, charging the chucked magnesium ingot into a crucible communicating with a molten metal transfer pipe and controlled for a melt level of molten magnesium therein, transferring molten magnesium to be delivered from the crucible through the transfer pipe and supplied to an injection sleeve before a shot of supplied molten magnesium for a die casting, lowering the chucked magnesium ingot to be partially dipped and melted in molten magnesium in the crucible, as the melt level is lowered, repeating the transferring molten magnesium, repeating the lowering the chucked magnesium ingot, and releasing the dipped magnesium ingot into molten magnesium in the crucible.
According to this aspect, a melt level can be controlled in a facilitated manner.